Role Of Long-range Interactions Research Articles

Mechanosensitivity of phase separation in an elastic gel

Liquid–liquid phase separation (LLPS) in binary or multi-component solutions is a well-studied subject in soft matter with extensive applications in biological systems. In recent years, several experimental studies focused on LLPS of solutes in hydrated gels, where the formation of coexisting domains induces elastic deformations within the gel. While the experimental studies report unique physical characteristics of these systems, such as sensitivity to mechanical forces and stabilization of multiple, periodic phase-separated domains, the theoretical understanding of such systems and the role of long-range interactions have not emphasized the nonlinear nature of the equilibrium binodal for strong segregation of the solute. In this paper, we formulate a generic, mean-field theory of a hydrated gel in the presence of an additional solute which changes the elastic properties of the gel. We derive equations for the equilibrium binodal of the phase separation of the solvent and solute and show that the deformations induced by the solute can result in effective long-range interactions between phase-separating solutes that can either enhance or, in the case of externally applied pressure, suppress phase separation of the solute relative to the case where there is no gel. This causes the coexisting concentrations at the binodal to depend on the system-wide average concentration, in contrast to the situation for phase separation in the absence of the gel.Graphical abstract

Role of long-range interaction on the electrical transport and electron–phonon scattering in thermoelectric Mg2Si

Many thermoelectrics are polar materials, where the long-range interaction plays a non-negligible role; however, its effect on the electrical transport property of thermoelectric materials is yet to be fully investigated. In this work, we demonstrate the importance of long-range interaction on the electrical transport property and the electron–phonon scattering mechanism in thermoelectric Mg2Si. We find that agreement between experimental and theoretical electrical conductivities can be significantly improved after considering the long-range interaction. In addition, we also demonstrate the importance of long-range interaction for studying the effect of band convergence on thermoelectric properties.

Designing BH3-Mimetic Peptide Inhibitors for the Viral Bcl-2 Homologues A179L and BHRF1: Importance of Long-Range Electrostatic Interactions.

Viruses have evolved strategies to prevent apoptosis of infected cells at early stages of infection. The viral proteins (vBcl-2s) from specific viral genes adopt a helical fold that is structurally similar to that of mammalian antiapoptotic Bcl-2 proteins and exhibit little sequence similarity. Hence, vBcl-2 homologues are attractive targets to prevent viral infection. However, very few studies have focused on developing inhibitors for vBcl-2 homologues. In this study, we have considered two vBcl-2 homologues, A179L from African swine fever virus and BHRF1 from Epstein–Barr virus. We generated two sets of 8000 randomized BH3-like sequences from eight wild-type proapoptotic BH3 peptides. During this process, the four conserved hydrophobic residues and an Asp residue were retained at their respective positions, and all other positions were substituted randomly without any bias. We constructed 8000 structures each for A179L and BHRF1 in complex with BH3-like sequences. Histograms of interaction energies calculated between the peptide and the protein resulted in negatively skewed distributions. The BH3-like peptides with high helical propensities selected from the negative tail of the respective interaction energy distributions exhibited more favorable interactions with A179L and BHRF1, and they are rich in basic residues. Molecular dynamics studies and electrostatic potential maps further revealed that both acidic and basic residues favorably interact with A179L, while only basic residues have the most favorable interactions with BHRF1. As in mammalian homologues, the role of long-range interactions and nonhotspot residues has to be taken into account while designing specific BH3-mimetic inhibitors for vBcl-2 homologues.

Droplet tilings for rapid exploration of spatially constrained many-body systems

Geometry in materials is a key concept which can determine material behavior in ordering, frustration, and fragmentation. More specifically, the behavior of interacting degrees of freedom subject to arbitrary geometric constraints has the potential to be used for engineering materials with exotic phase behavior. While advances in lithography have allowed for an experimental exploration of geometry on ordering that has no precedent in nature, many of these methods are low throughput or the underlying dynamics remain difficult to observe directly. Here, we introduce an experimental system that enables the study of interacting many-body dynamics by exploiting the physics of multidroplet evaporation subject to two-dimensional spatial constraints. We find that a high-energy initial state of this system settles into frustrated, metastable states with relaxation on two timescales. We understand this process using a minimal dynamical model that simulates the overdamped dynamics of motile droplets by identifying the force exerted on a given droplet as being proportional to the two-dimensional vapor gradients established by its neighbors. Finally, we demonstrate the flexibility of this platform by presenting experimental realizations of droplet-lattice systems representing different spin degrees of freedom and lattice geometries. Our platform enables a rapid and low-cost means to directly visualize dynamics associated with complex many-body systems interacting via long-range interactions. More generally, this platform opens up the rich design space between geometry and interactions for rapid exploration with minimal resources.

Role of long-range interaction on the photon-excited η-pairing of electrons

We report studies on the influence of a time-dependent external driving fields of the photons on a quantum system described by Hubbard model with long-range interactions. Through the exact diagonalization method to calculate the superconducting pair correlation functions, we show that a weak repulsive long-range Coulomb interaction can help enhance superconducting pair correlation function in some parameter space, which may appear in cuprates, while the number of doublons is increased by the attractive long-range interaction. Out of the parameter space, long-range interaction can be harmful to η-pairing and on-site pairing of electrons. Our results may help people find and design new materials with significant enhancement of transient superconductivity induced by light pulse irradiations.

Development of 3D neuromuscular bioactuators.

Neuronal control of skeletal muscle bioactuators represents a critical milestone toward the realization of future biohybrid machines that may generate complex motor patterns and autonomously navigate through their environment. Animals achieve these feats using neural networks that generate robust firing patterns and coordinate muscle activity through neuromuscular units. Here, we designed a versatile 3D neuron-muscle co-culture platform to serve as a test-bed for neuromuscular bioactuators. We used our platform in conjunction with microelectrode array electrophysiology to study the roles of synergistic interactions in the co-development of neural networks and muscle tissues. Our platform design enables co-culture of a neuronal cluster with up to four target muscle actuators, as well as quantification of muscle contraction forces. Using engineered muscle tissue targets, we first demonstrated the formation of functional neuromuscular bioactuators. We then investigated possible roles of long-range interactions in neuronal outgrowth patterns and observed preferential outgrowth toward muscles compared to the acellular matrix or fibroblasts, indicating muscle-specific chemotactic cues acting on motor neurons. Next, we showed that co-cultured muscle strips exhibited significantly higher spontaneous contractility as well as improved sarcomere assembly compared to muscles cultured alone. Finally, we performed microelectrode array measurements on neuronal cultures, which revealed that muscle-conditioned medium enhances overall neural firing rates and the emergence of synchronous bursting patterns. Overall, our study illustrates the significance of neuron-muscle cross talk for the in vitro development of neuromuscular bioactuators.

Spontaneous shrinking of soft nanoparticles boosts their diffusion in confined media

Improving nanoparticles (NPs) transport across biological barriers is a significant challenge that could be addressed through understanding NPs diffusion in dense and confined media. Here, we report the ability of soft NPs to shrink in confined environments, therefore boosting their diffusion compared to hard, non-deformable particles. We demonstrate this behavior by embedding microgel NPs in agarose gels. The origin of the shrinking appears to be related to the overlap of the electrostatic double layers (EDL) surrounding the NPs and the agarose fibres. Indeed, it is shown that screening the EDL interactions, by increasing the ionic strength of the medium, prevents the soft particle shrinkage. The shrunken NPs diffuse up to 2 orders of magnitude faster in agarose gel than their hard NP counterparts. These findings provide valuable insights on the role of long range interactions on soft NPs dynamics in crowded environments, and help rationalize the design of more efficient NP-based transport systems.

On the thermal equilibrium state of large-scale flows

In a forced three-dimensional turbulent flow the scales larger than the forcing scale have been conjectured to reach a thermal equilibrium state forming a $k^{2}$ energy spectrum, where $k$ is the wavenumber. In this work we examine the properties of these large scales in turbulent flows with the use of numerical simulations. We show that the choice of forcing can strongly affect the behaviour of the large scales. A spectrally dense forcing (a forcing that acts on all modes inside a finite-width spherical shell) with long correlation times may lead to strong deviations from the $k^{2}$ energy spectrum, while a spectrally sparse forcing (a forcing that acts only on a few modes) with short correlated time scale can reproduce the thermal spectrum. The origin of these deviations is analysed and the involved mechanisms is unravelled by examining: (i) the number of triadic interactions taking place, (ii) the spectrum of the nonlinear term, (iii) the amplitude of interactions and the fluxes due to different scales and (iv) the transfer function between different shells of wavenumbers. It is shown that the spectrally dense forcing allows for numerous triadic interactions that couple one large-scale mode with two forced modes and this leads to an excess of energy input at the large scales. This excess of energy is then moved back to the small scales by self-interactions of the large-scale modes and by interactions with the turbulent small scales. The overall picture that arises from the present analysis is that the large scales in a turbulent flow resemble a reservoir that is in (non-local) contact with a second out-of-equilibrium reservoir consisting of the smaller (forced, turbulent and dissipative) scales. If the injection of energy at the large scales from the forced modes is relative weak (as is the case for the spectrally sparse forcing) then the large-scale spectrum remains close to a thermal equilibrium and the role of long-range interactions is to set the global energy (temperature) of the equilibrium state. If, on the other hand, the long-range interactions are dominant (as is the case for the spectrally dense forcing), the large-scale self-interactions cannot respond fast enough to bring the system into equilibrium. Then the large scales deviate from the equilibrium state with energy spectrum that may display exponents different from the $k^{2}$ spectrum.

Competition between phase separation and spin density wave or charge density wave order: Role of long-range interactions

Recent studies of pairing and charge order in materials such as FeSe, SrTiO$_3$, and 2H-NbSe$_2$ have suggested that momentum dependence of the electron-phonon coupling plays an important role in their properties. Initial attempts to study Hamiltonians which either do not include or else truncate the range of Coulomb repulsion have noted that the resulting spatial non-locality of the electron-phonon interaction leads to a dominant tendency to phase separation. Here we present Quantum Monte Carlo results for such models in which we incorporate both on-site and intersite electron-electron interactions. We show that these can stabilize phases in which the density is homogeneous and determine the associated phase boundaries. As a consequence, the physics of momentum dependent electron-phonon coupling can be determined outside of the trivial phase separated regime.

Epidemic Dynamics in Open Quantum Spin Systems.

We explore the nonequilibrium evolution and stationary states of an open many-body system that displays epidemic spreading dynamics in a classical and a quantum regime. Our study is motivated by recent experiments conducted in strongly interacting gases of highly excited Rydberg atoms where the facilitated excitation of Rydberg states competes with radiative decay. These systems approximately implement open quantum versions of models for population dynamics or disease spreading where species can be in a healthy, infected or immune state. We show that in a two-dimensional lattice, depending on the dominance of either classical or quantum effects, the system may display a different kind of nonequilibrium phase transition. We moreover discuss the observability of our findings in laser driven Rydberg gases with particular focus on the role of long-range interactions.

Deciphering the Role of Long-Range Interaction in Endohedral Metallofullerenes: A Revisit to Sc2C70

Structure elucidation is a vital step to study endohedral metallofullerene (EMF), and theoretical investigation is a useful complementary way to elucidate structures of EMFs. However, our recent work exposed that density functional theory (DFT) methods without long-range corrections are prone to overestimate energies of Sc2C2@C72 isomers. In this work, the role of long-range interaction in energy estimation of EMFs was rigorously investigated by comparing energies and interaction energies of Sc2C70 and La2C96 series with wB97XD, M06-2X, B3LYP, and PBE0 methods, and it was disclosed that long-range interaction is ubiquitously imperative for metal cluster fullerenes and conventional metallofullerenes whose cages are absent of adjacent pentagon pair(s). Meanwhile, thermodynamic stabilities of the controversial Sc2C70 series were thoroughly investigated, and Sc2C2@C2v(6073)-C68 with the highest abundance on the temperature range of EMF formation instead of Sc2@C2v(7854)-C70 was confirmed to be the experimenta...

From mechanical to biological oscillator networks: The role of long range interactions

The study of one-dimensional particle networks of Classical Mechanics, through Hamiltonian models, has taught us a lot about oscillations of particles coupled to each other by nearest neighbor (short range) interactions. Recently, however, a careful analysis of the role of long range interactions (LRI) has shown that several widely accepted notions concerning chaos and the approach to thermal equilibrium need to be modified, since LRI strongly affects the statistics of certain very interesting, long lasting metastable states. On the other hand, when LRI (in the form of non-local or all-to-all coupling) was introduced in systems of biological oscillators, Kuramoto’s theory of synchronization was developed and soon thereafter researchers studied amplitude and phase oscillations in networks of FitzHugh Nagumo and Hindmarsh Rose (HR) neuron models. In these models certain fascinating phenomena called chimera states were discovered where populations of synchronous and asynchronous oscillators are seen to coexist in the same system. Currently, their synchronization properties are being widely investigated in HR mathematical models as well as realistic neural networks, similar to what one finds in simple living organisms like the C.elegans worm.

Publisher's Note: Charge avalanches and depinning in the Coulomb glass: The role of long-range interactions [Phys. Rev. B93, 094429 (2016)

Publisher's Note: Charge avalanches and depinning in the Coulomb glass: The role of long-range interactions [Phys. Rev. B<b>93</b>, 094429 (2016)

Enhanced growth rates of nanodroplets in the free molecular regime: The role of long-range interactions

Recently, Pathak et al. Citation(2013) conducted a series of non-isothermal D2O nanodroplet growth studies in the free molecular regime. They found that under highly non-equilibrium conditions, the condensation (qc) and evaporation coefficients (qe) can differ from each other and from the expected value of 1. Here, we confirm these observations by analyzing comparable experiments using n-propanol. We show that the best agreement with the non-isothermal Hertz–Knudsen growth law corresponds to setting (qc, qe) = (1, 0.6) or (qc, qe) = (1.3, 1). The approach of retarded evaporation yields values close to those observed by Pathak et al. for D2O, but is difficult to justify theoretically. Enhancing the condensation coefficient is consistent with long-range attractive interactions between the vapor molecules and droplets in the nanometer size range.© 2016 American Association for Aerosol Research

Charge avalanches and depinning in the Coulomb glass: The role of long-range interactions

We explore the stability of far-from-equilibrium metastable states of a three-dimensional Coulomb glass at zero temperature by studying charge avalanches triggered by a slowly varying external electric field. Surprisingly, we identify a sharply defined dynamical ("depinning") phase transition from stationary to nonstationary charge displacement at a critical value of the external electric field. Using particle-conserving dynamics, scale-free system-spanning avalanches are observed only at the critical field. We show that the qualitative features of this depinning transition are completely different for an equivalent short-range model, highlighting the key importance of long-range interactions for nonequilibrium dynamics of Coulomb glasses.

From coherent shocklets to giant collective incoherent shock waves in nonlocal turbulent flows.

Understanding turbulent flows arising from random dispersive waves that interact strongly through nonlinearities is a challenging issue in physics. Here we report the observation of a characteristic transition: strengthening the nonlocal character of the nonlinear response drives the system from a fully turbulent regime, featuring a sea of coherent small-scale dispersive shock waves (shocklets) towards the unexpected emergence of a giant collective incoherent shock wave. The front of such global incoherent shock carries most of the stochastic fluctuations and is responsible for a peculiar folding of the local spectrum. Nonlinear optics experiments performed in a solution of graphene nano-flakes clearly highlight this remarkable transition. Our observations shed new light on the role of long-range interactions in strongly nonlinear wave systems operating far from thermodynamic equilibrium, which reveals analogies with, for example, gravitational systems, and establishes a new scenario that can be common to many turbulent flows in photonic quantum fluids, hydrodynamics and Bose–Einstein condensates.

On the role of long range interactions for the adsorption of sexithiophene on Ag(110) surface.

The adsorption characteristics of the sexithiophene (6T) molecule on Ag(110) are studied using density functional theory with the inclusion of van der Waals (vdW) interactions. The stable adsorption configurations on 6T on Ag(110) as well as the nature of bonding the Ag substrate are evaluated. We also assess the performance of the vdW-DF method in describing the adsorption, energetics, heights, as well as the interface characteristics with the Ag(110) surface. We find two lowest adsorption energy configurations, at which the 6T molecule aligns with its molecular long axis parallel and perpendicular to the [001] direction, to be energetically close to each other, suggesting that they may coexist. Our findings indicate a significant increase in the 6T adsorption energies upon the inclusion of vdW interactions with the highest increase obtained using the opt-type functionals, in particular with the optB86b-vdW functional. The revPBE-vdW and rPW86-vdW2 functionals lead to less enhancement in adsorption energies that is attributed to the strong repulsive nature of these functionals, in agreement with earlier predictions. Upon adsorption of the 6T molecule, the changes in the atomic and electronic structures of the 6T molecule and Ag surface are found to be negligible; there is no charge transfer, and no interface state is observed. The work function is reduced upon adsorption with the largest change is ~0.6 eV obtained using the optB88-vdW functional. The results are in good agreement with the available experimental observations of the adsorption configurations and the work function changes. Based on our results, we conclude that the nature of bonding for 6T on Ag(110) can be classified as strong physisorption.

Inhomogeneities and impurities in a dense one-dimensional Rydberg lattice gas

We consider a dense one-dimensional laser-driven Rydberg lattice gas with perfect nearest-neighbor blockade. The ground state of this system can be found analytically in certain parameter regimes even when the applied fields are inhomogeneous in space. We will use this unique feature to investigate the effect of an impurity---introduced by the local variation of the laser parameters---on the correlations of the many-body ground state. Moreover, we explore the role of a staggered laser field which alternates from site to site thereby breaking the sublattice symmetry. We demonstrate that this technique, which can be applied experimentally, reveals insights into the role of long-range interactions on the critical properties of a Rydberg gas. Our work highlights possibilities for the exploration of many-body physics in Rydberg lattice gases based on locally tunable laser fields.

Exact entanglement studies of strongly correlated systems: role of long-range interactions and symmetries of the system

We study the bipartite entanglement of strongly correlated systems using exact diagonalization techniques. In particular, we examine how the entanglement changes in the presence of long-range interactions by studying the Pariser–Parr–Pople model with long-range interactions. We compare the results for this model with those obtained for the Hubbard and Heisenberg models with short-range interactions. This study helps us to understand why the density matrix renormalization group (DMRG) technique is so successful even in the presence of long-range interactions. To better understand the behavior of long-range interactions and why the DMRG works well with it, we study the entanglement spectrum of the ground state and a few excited states of finite chains. We also investigate if the symmetry properties of a state vector have any significance in relation to its entanglement. Finally, we make an interesting observation on the entanglement profiles of different states (across the energy spectrum) in comparison with the corresponding profile of the density of states. We use isotropic chains and a molecule with non-Abelian symmetry for these numerical investigations.

The role of long-range interactions in the phase behavior of ionic liquids

The COSMO-type liquid activity coefficient models are among the most successful methods for the prediction of the phase behaviours of fluids containing ionic liquids. However, these models consider only interactions between species that are in close contact; in other words, the long-range Coulomb interactions, which are known to be important for systems containing charged species, are completely ignored. Here we show that the inclusion of long-range terms (with, e.g., the Pitzer-Debye-Hückel model) is indeed critical to obtain the correct osmotic coefficients and the asymptotic behaviours in the infinite dilution of IL solutions. However, the direct combination of PDH and COSMO-type models does not produce accurate activity coefficient over the whole concentration range because both models contain short range interactions. We show that a recent revision of the COSMO-SAC model, which includes the PDH contributions and a specific treatment of solvent-ion and ion-ion interactions, is capable of providing an accurate description of the properties (phase behaviour, osmotic coefficients) of aqueous IL solutions over the whole concentration range.